WO2018009021A1

WO2018009021A1 - Method and apparatus for executing handover in wireless communication system

Info

Publication number: WO2018009021A1
Application number: PCT/KR2017/007292
Authority: WO
Inventors: 류승보; 김대중; 장훈; 전남열
Original assignee: 삼성전자 주식회사
Priority date: 2016-07-08
Filing date: 2017-07-07
Publication date: 2018-01-11
Also published as: US11843941B2; US20190253942A1; KR20180006236A; KR102502279B1; US20220232374A1; EP3454603A1; US11323874B2; US20240107298A1; EP3454603A4

Abstract

The present invention relates to a 5G or pre-5G communication system for supporting higher data transmission rate beyond the 4G communication system such as LTE. A handover method for a terminal according to one embodiment of the present invention comprises the steps of: receiving, from a source cell, a message comprising information for one or more target cells for carrying out a fast handover; and carrying out a fast handover by reusing a wireless bearer on the basis of the received information.

Description

Method and apparatus for performing handover in wireless communication system

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for improving a handover procedure when a terminal moves between cells.

In order to meet the increasing demand for wireless data traffic since the commercialization of 4G communication systems, efforts are being made to develop improved 5G communication systems or pre-5G communication systems. For this reason, a 5G communication system or a pre-5G communication system is called a Beyond 4G network communication system or a post LTE system.

In order to achieve high data rates, 5G communication systems are being considered for implementation in the ultra-high frequency (mmWave) band (eg, such as the 60 Gigabit (60 GHz) band). In order to mitigate the path loss of radio waves in the ultra-high frequency band and increase the propagation distance of radio waves, beamforming, massive array multiple input / output (FD-MIMO), and FD-MIMO are used in 5G communication systems. Array antenna, analog beam-forming, and large scale antenna techniques are discussed.

In addition, in order to improve the network of the system, in the 5G communication system, an advanced small cell, an advanced small cell, a cloud radio access network (cloud RAN), an ultra-dense network ), Device to Device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation Technology development, etc.

In addition, in 5G systems, Hybrid FSK and QAM Modulation (FQAM) and Slide Window Superposition Coding (SWSC), Advanced Coding Modulation (ACM), and FBMC (Filter Bank Multi Carrier) and NOMA are advanced access technologies. (non orthogonal multiple access), and sparse code multiple access (SCMA) are being developed.

Meanwhile, in a handover procedure in which a terminal moves between cells, there is a need for a method for improving performance of a terminal by minimizing an inefficient process.

In view of the above necessity, in the present invention, latency is reduced and performance is minimized by minimizing inefficient processes such as user plane reset or security key update that may occur during handover in a wireless communication system. It provides a method and apparatus that can perform this enhanced handover.

According to an embodiment of the present invention, in a handover method of a terminal in a wireless communication system, a message including information on at least one target cell for fast handover is performed from a source cell And reusing the radio bearer based on the received information to perform the fast handover.

Meanwhile, according to another embodiment of the present invention, in a handover method of a source cell in a wireless communication system, receiving a measurement report including a measurement result for at least one cell from a terminal, the measurement Based on the report, the method may include determining at least one target cell capable of performing fast handover that reuses the radio bearer, and transmitting information on the determined at least one target cell to the terminal. have.

Meanwhile, according to another embodiment of the present invention, in a handover method of a target cell in a wireless communication system, receiving a handover message including a new terminal identifier from a terminal when a fast handover is completed And a security key corresponding to a source cell, a service data adaptation protocol (SDAP), a packet data convergence protocol (PDCP), and a radio link based on the new terminal identifier of the received message. The method may include reusing a radio bearer of a specific user plane protocol such as radio link control (RLC), medium access control, and physical layer.

According to an embodiment of the present invention, the terminal may perform handover with reduced latency and improved performance.

1 is a sequence diagram illustrating a terminal based handover procedure according to a general method;

2 is a sequence diagram illustrating a network-based handover procedure according to a general method;

3 is a sequence diagram illustrating an inter-cell handover procedure in a terminal-based base station according to an embodiment of the present invention;

4 is a sequence diagram showing a terminal-based base station handover procedure according to an embodiment of the present invention;

5 is a flowchart illustrating a terminal-based handover procedure of a terminal according to an embodiment of the present invention;

6 is a flowchart illustrating an inter-cell handover procedure in a terminal-based base station of a source cell according to an embodiment of the present invention;

7 is a flowchart illustrating an inter-base station handover procedure based on a terminal of a base station according to an embodiment of the present invention;

8 is a sequence diagram illustrating an inter-cell handover procedure in a network-based base station according to an embodiment of the present invention.

9 is a sequence diagram showing a network-based base station handover procedure according to an embodiment of the present invention;

10 is a flowchart illustrating a network-based handover procedure of a terminal according to an embodiment of the present invention;

11 is a flowchart illustrating an inter-cell handover procedure in a network-based base station of a base station according to an embodiment of the present invention;

12 is a flowchart illustrating a network-based handover procedure between base stations according to an embodiment of the present invention;

13 is a block diagram showing a configuration of a terminal according to an embodiment of the present invention;

14 is a block diagram illustrating a configuration of a base station according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In describing the embodiments herein, descriptions of technical contents that are well known in the technical field to which the present invention belongs and are not directly related to the present invention will be omitted. This is to more clearly communicate without obscure the subject matter of the present invention by omitting unnecessary description.

For the same reason, in the accompanying drawings, some components are exaggerated, omitted or schematically illustrated. In addition, the size of each component does not fully reflect the actual size. The same or corresponding components in each drawing are given the same reference numerals.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments of the present invention make the disclosure of the present invention complete and the general knowledge in the technical field to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

At this point, it will be appreciated that each block of the flowchart illustrations and combinations of flowchart illustrations may be performed by computer program instructions. Since these computer program instructions may be mounted on a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, those instructions executed through the processor of the computer or other programmable data processing equipment may be described in flow chart block (s). It creates a means to perform the functions. These computer program instructions may be stored in a computer usable or computer readable memory that can be directed to a computer or other programmable data processing equipment to implement functionality in a particular manner, and thus the computer usable or computer readable memory. It is also possible for the instructions stored in to produce an article of manufacture containing instruction means for performing the functions described in the flowchart block (s). Computer program instructions may also be mounted on a computer or other programmable data processing equipment, such that a series of operating steps may be performed on the computer or other programmable data processing equipment to create a computer-implemented process to create a computer or other programmable data. Instructions for performing the processing equipment may also provide steps for performing the functions described in the flowchart block (s).

In addition, each block may represent a portion of a module, segment, or code that includes one or more executable instructions for executing a specified logical function (s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of order. For example, the two blocks shown in succession may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the corresponding function.

In this case, the term '~ part' used in the present embodiment refers to software or a hardware component such as an FPGA or an ASIC, and '~ part' plays certain roles. However, '~' is not meant to be limited to software or hardware. May be configured to reside in an addressable storage medium or may be configured to play one or more processors. Thus, as an example, '~' means components such as software components, object-oriented software components, class components, and task components, and processes, functions, properties, procedures, and the like. Subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functionality provided within the components and the 'parts' may be combined into a smaller number of components and the 'parts' or further separated into additional components and the 'parts'. In addition, the components and '~' may be implemented to play one or more CPUs in the device or secure multimedia card.

In the present invention, the terminal may generally include a mobile terminal, and may indicate a device that is subscribed to the mobile communication system and receives a service from the mobile communication system. The mobile terminal may include a smart device such as a smart phone, a tablet PC, which corresponds to an example and the present invention is not limited thereto.

The cellular wireless communication system performs a handover procedure when the serving cell of the mobile terminal needs to be changed. For example, when a terminal communicating with a source cell is difficult to perform communication due to an interruption, or when the terminal moves from an area within a source cell to an area of a target cell. A handover may be performed to the target cell.

Hereinafter, a general handover procedure of a terminal will be described with reference to FIGS. 1 and 2.

FIG. 1 is a sequence diagram illustrating a general UE-based handover method. In detail, the terminal 100 performs a handover process from the source cell 200 to the target cell 300. The source cell 200 and the target cell 300 may be cells for one base station or cells of different base stations.

First, in step S110, the terminal 100 may transmit a measurement report to the source cell 200. For example, the terminal 100 connecting to the source cell 200 and performing communication may periodically measure the signal level and report it to the source cell 200. In more detail, the terminal 100 may be set for a preset condition or report period for the measurement report. In addition, the terminal 100 may perform the measurement report according to the setting when the preset condition is satisfied or according to a preset reporting period.

If the source cell 200 and the target cell 300 are cells of different base stations (for example, inter-handover), in step S115, the source cell 200 sends a pre-handover request message to the target cell 300. Can be transmitted. In operation S120, the target cell 300 may transmit a response to the received pre-handover request message.

For example, the source cell 200 may request UE-based handover to the target cell 300 in advance through a pre-handover request message. If it is determined that the target cell 300 that has received the advance request can accept the handover, the target cell 300 transmits an Ack message for the handover advance request to the source cell 200 to perform the handover. You can accept

Meanwhile, the steps S115 and S120 may be omitted when handover between cells in the base station is performed. For example, when the source cell 200 and the target cell 300 are cells of one base station, it is not necessary to transmit and receive a pre-handover request message and response based on the measurement report of the terminal between the cells.

In operation S125, the source cell 200 may provide candidate cell information that the terminal 100 can use in determining handover through an RRC connection reconfiguration message to the terminal 100.

For example, as described above, at least one target cell transmitting the Ack message for the handover advance request may be a candidate cell. Accordingly, the source cell 200 may include information on at least one target cell that has transmitted an Ack message for handover pre-request in an RRC connection reconfiguration message. For example, the source cell 200 may transmit a cell ID as information on the target cell.

In step S130, if the handover event is triggered, the terminal 100 may determine the handover. For example, the terminal 100 may determine a target cell to perform handover based on the candidate cell information.

When the handover to the target cell 300 is determined by the terminal 100, the terminal 100 may perform initial access with the target cell 300 through a random access procedure.

For example, in step S135, the terminal 100 may transmit a random access preamble to the target cell 300. In response to the random access preamble, in step S140, the terminal 100 may receive a random access response message from the target cell 300.

In step S145, the terminal 100 transmits an RRC connection reestablishment request message to the target cell 300, and receives an RRC connection reestablishment message in step S150. Can be.

By the above-described process, each of the terminal 100 and the target cell 300 to which the connection is completed, in step S155 and S160, service data adaptation protocol (SDAP), packet data convergence protocol (packet data convergence protocol) , PDCP), radio link control (RLC), medium access control, and radio bearer (RB) of physical layer (Release) and then re-establish (Establishment) can do.

Specifically, each of the terminal 100 and the target cell 300 resets a packet data unit (PDU) existing in the user plane protocol stack (for example, RLC and PDCP).

In operation S165 and operation S170, each of the terminal 100 and the target cell 300 may update a security key.

For example, the source cell 200 may update the security key using the cell ID (PCID) of the target cell 300 and transmit the updated security key to the target cell 300. . Therefore, the target cell 300 receiving the updated security key can be used to encrypt or decrypt data transmitted and received using the updated security key.

In addition, the source cell 200 may transmit parameters for updating the security key from the terminal 100. The terminal 100 may generate an updated security key by using the information received from the source cell 200. After completing the handover procedure, the terminal 100 may encrypt or decrypt data transmitted and received using the updated security key.

In operation S175, the terminal 100 may transmit an RRC connection reestablishment complete message to the target cell 300.

2 is a sequence diagram illustrating a network-based (NW-based) handover procedure according to a general method. In FIG. 2, a description will be given of differences from the UE-based handover procedure described with reference to FIG. 1.

First, in step S210, the terminal 100 may transmit a measurement report (measurement report) to the source cell 200.

In operation S215, the source cell 200 may determine handover. For example, the source cell 200 may determine a target cell to perform handover based on the measurement report received from the terminal 100.

When the source cell 200 and the target cell 300 are cells of different base stations, in step S220, the source cell 200 may transmit a handover request to the target cell 300. In this case, the source cell 200 may transmit the updated security key based on the cell ID (PCID) of the target cell 300.

In operation S225, the target cell 300, which determines that the handover is acceptable, may transmit a handover request response to the source cell 200.

Steps S220 and S225 are necessary procedures only when handover between base stations is performed because the source cell 200 and the target cell 300 are cells of different base stations. Therefore, when the source cell 200 and the target cell 300 are cells of the same base station, the steps S220 and S225 may be omitted.

In operation S230, the source cell 200 receiving the handover request response may transmit an RRC connection reconfiguration message including movement control information to the terminal 100. In this case, the source cell 200 may transmit information on the target cell 300 to perform handover to the terminal 100.

Meanwhile, when the source cell 200 and the target cell 300 are cells of different base stations, in step S235, the source cell 200 goes to the target cell 300 in sequence number status. SNstatus) can be sent. Specifically, the source cell 200 transmits the sequence number of the packet of the PDCP layer to the target cell 300 through the interface between the base stations, to inform which packet to transmit and receive from the terminal 100 after the handover is completed. Can be.

In step S235, since the source cell 200 and the target cell 300 are cells of different base stations, the step S235 is a necessary procedure only when inter-handover between base stations is performed. Therefore, when the source cell 200 and the target cell 300 are cells of the same base station, step S235 may be omitted.

On the other hand, each of the terminal 100 and the target cell 300, in step S240 and S245, service data adaptation protocol (SDAP), packet data convergence protocol (PDCP), radio link control A radio bearer (RB) of a radio link control (RLC), a medium access control, and a physical layer may be reset.

In operation S250 and operation S255, the terminal 100 and the target cell 300 may each update a security key.

In operation S260, the terminal 100 may transmit a random access preamble to the target cell 300. In response to the random access preamble, in step S265, the terminal 100 may receive a random access response message from the target cell 300.

In operation S270, the terminal 100 may complete the connection with the target cell 300 by transmitting an RRC connection reconfiguration complete message to the target cell 300.

In the UE-based and NW-based handover process as shown in FIGS. 1 and 2, the radio bearer established in the source cell may be reset and reestablished in the target cell. By reestablishment, user data of the user plane protocol stack (eg PDCP and RLC) can also be reset.

In addition, when the cell is changed through handover, the security key is updated. Therefore, even if user data encrypted using the security key in the PDCP layer is transmitted to the target cell, the updated security key cannot be decrypted.

On the other hand, when performing communication in the high frequency band (ex. 28GHz), such as 5G system, due to the impossibility of communication with the source cell due to the worsening of the wireless environment due to a temporary obstacle between the base station and the terminal providing the communication service, The terminal may frequently handover to a target cell.

At this time, handover performance is important, and one of the performance factors may be referred to as handover setup time. However, as described above, in general, a security key must be changed every time a cell is changed, and an inefficient structure of resetting existing user data is required. Therefore, there is a problem that high speed handover is difficult to be performed.

Hereinafter, a handover method for solving the above problems will be described in detail.

3 is a sequence diagram illustrating an intra-handover procedure in a terminal-based base station according to an embodiment of the present invention.

First, in step S310, the terminal 100 may transmit a measurement report (measurement report) to the source cell 200.

In step S315, the source cell 200 may transmit an RRC connection reconfiguration message to the terminal 100. In this case, the source cell 200 may provide candidate cell information that the terminal 100 can use when determining handover through the RRC connection reconfiguration message.

For example, the source cell 200 may transmit information about candidate cells to which the terminal 100 can handover to the terminal 100 based on the measurement report. The candidate cells may include candidate cells capable of at least one fast HO.

Accordingly, the source cell 200 is information on a candidate cell capable of the fast HO in the candidate cell information, and a new terminal ID (for example, a target cell for fast handover) is fast. An identifier (C-RNTI) to allocate, system information (SI) for the target cell, RACH information, and user protocol information to be reused according to a central unit (CU) -access unit (AU) function split option Can be sent. The user protocol setting to be reused by specifying in the target cell during the fast HO may be configured by, for example, the following combination.

-Reuse only PDCP Protocol

-Reuse only PDCP, RLC Protocol

-Reuse only PDCP, RLC, MAC Protocol

-Reuse only PDCP, RLC, MAC, PHY Protocol

-Reuse only SDAP, PDCP Protocol

-Reuse only SDAP, PDCP, RLC Protocol

-Reuse only SDAP, PDCP, RLC, MAC Protocol

-SDAP, PDCP, RLC, MAC, PHY Protocol reuse

Specific examples of the candidate cell information are shown in Table 1 below.

Table 1

Candidate Cell Info	Description	Option	Condition
candidateCellID	Candidate Cell Physical Cell ID	Mandatory	Required for UE-based HO (Normal, Fast HO)
newUE-Identity	C-RNTI of Candidate Cell	OPTIONAL	Required for UE-based Fast HO
radioResourceConfigCommon	Candidate Cell's common radio resource configurations	OPTIONAL	Required for UE-based Fast HO
rach-ConfigDedicated	Candidate Cell dedicated random access parameters	OPTIONAL	Select from UE-based Fast HO
ReuseProtocolType	Target protocol (SDAP, PDCP, RLC, MAC, PHY) to be reused without resetting during fast handover	Mandatory	Required for UE-based HO (Normal, Fast HO)

Meanwhile, in step S320, when the handover event is triggered and the target cell is determined, the terminal 100 may determine whether the fast HO is based on candidate cell information of the determined target cell. For example, the terminal 100 may be preset to perform fast HO when performing handover between cells in the base station. Accordingly, the terminal 100 may determine to perform fast HO on a cell of a base station such as the source cell 200 based on the candidate cell information.

In the case of Fast HO, the UE may maintain a security key as a key used in the source cell without resetting specific user plane protocols (ie, PDCP, RLC, MAC, and PHY) according to the application of the Reuse Protocol.

The terminal 100 performs a random access process with the target cell, and may perform dedicated random access or contention-based random access according to whether or not rach-ConfigDedicated is set in the candidate cell information. have.

In detail, in operation S325, the terminal 100 that has determined fast HO to the target cell 300 may transmit a random access preamble to the target cell 300. In response to the random access preamble, in step S330, the terminal 100 may receive a random access response message from the target cell 300.

When the random access procedure is completed, in step S335, the terminal 100 transmits to the target cell 300 an RRC connection reconfiguration complete message including C-RNTI information of a candidate cell as a new terminal identifier. Can be transmitted.

Accordingly, the target cell 300 may reuse the specific user plane protocol (eg PDCP / RLC) release and security key of the source cell 200 without resetting using the received new terminal identifier. For example, the target cell 300 may use the security key of the source cell as it is. In addition, the target cell 300 may not perform a reset for a specific user plane protocol (eg PDCP / RLC) release.

4 is a sequence diagram illustrating an inter-handover procedure between UE-based base stations according to an embodiment of the present invention. Unlike FIG. 3, even when handover between cells of different base stations is performed, fast HO may be performed according to a preset condition. For example, if the service used by the terminal is a service (eg, a streaming service) that needs to send and receive data without interruption, or if there are many obstacles around, or handover is frequently repeated for an arbitrary time. In this case, it may be determined that the fast HO condition is satisfied.

First, the source cell 200 receiving the measurement report from the terminal 100 in step S410 may transmit a pre-handover request message to the target cell 300 in step S415. In operation S420, the target cell 300 may transmit a response to the received pre-handover request message.

In detail, the source cell 200 may transmit the RB of the user plane (eg, PDCP / RLC) and the security key of the source cell 200 in a pre-handover request message. Therefore, when fast HO is performed by the determination of the terminal 100, the target cell 300 may use the security key of the source cell 200.

If it is determined that the target cell 300 that has received the advance request can accept the handover, the target cell 300 transmits an Ack message for the handover advance request to the source cell 200 to perform the handover. You can accept

In step S425, the source cell 200 may provide candidate cell information that the terminal 100 can use when determining handover through an RRC connection reconfiguration message to the terminal 100. For example, the source cell 200 transmits a new terminal ID (for example, identifier (C-RNTI) assigned by a target cell), target SI, and RACH information for fast HO, including the candidate cell information. Can be.

In operation S430, the terminal 100 may determine handover. Specifically, when the handover event is triggered and the target cell is determined, the terminal 100 may determine whether the fast HO is based on the determined candidate cell information of the target cell.

The terminal 100 having fast HO determined as the target cell 300 may maintain a security key as a key used in the source cell without resetting a specific user plane protocol (for example, PDCP and RLC).

In addition, through step S435 to step S445, the random access procedure may be performed and an RRC connection reset complete message may be transmitted. The detailed process of steps S430 to S445 is as described above with reference to FIG. 3.

Therefore, the target cell 300 may also reuse the RB and the security key of a specific user plane protocol (eg PDCP and RLC) of the source cell 200 without resetting.

Meanwhile, in operation S450, the target cell 300 may transmit a fast handover indication to the source cell 200. Specifically, since the target cell 300 is a cell of a base station different from the source cell 200, the target cell 300 may receive the existing RLC RB by transmitting the fast HO indication.

Accordingly, the source cell 200 receiving the fast HO indication may transmit the SNstatus of the RLC to the target cell 300 in step S455. Accordingly, the target cell 300 can be reused without resetting the existing RLC RB.

The source cell 200 may forward the RLC packet having the SN following the SN of the data packet transmitted from the source cell to the target cell according to the SNstatus of the RLC. Hereinafter, detailed operations of the terminal and the base station in the UE-based fast HO as described above will be described with reference to FIGS. 5 to 7.

Specifically, FIG. 5 is a flowchart illustrating a UE-based fast HO procedure of a terminal according to an embodiment of the present invention. When the UE performs the UE-based fast HO, it may operate regardless of intra or inter HO.

In step S500, the terminal may transmit a measurement report (MR) to the source cell.

For example, the base station may set the measurement report to the terminal in order to select a candidate cell for terminal-based handover (hereinafter, UE-Based HO). Accordingly, the terminal may transmit a measurement report to the source cell.

In operation S510, the terminal may receive candidate target cell information for the UE-Based HO. In more detail, the base station may select at least one candidate cell that may become a target cell in the UE-based HO and transmit candidate cell information to the UE based on the MR. The attribute information of the candidate cell may include a new terminal identifier (newUE-Identity) including a candidate cell ID, radio resource configuration command (radioResourceConfigCommon) information, and RACH information (rach-ConfigDedicated).

On the other hand, if the fast HO is not performed, the source cell may transmit candidate cell information including only the candidate cell identifier to the terminal.

In step S520, the UE may determine the handover when the UE-Based HO event trigger occurs. In operation S530, the terminal may determine whether the target cell performing the handover is a target cell for fast handover.

For example, when a handover event is triggered to select a target cell, the terminal may determine whether a fast HO operation is performed based on candidate cell information of the target cell. For example, the terminal may receive information on candidate cells for UE-based OH from the base station. If there is a cell that needs fast HO among the candidate cells (for example, among other candidate cells among the candidate cells, it is determined that the fast HO is required, or the service used by the terminal is determined without interrupting data). Streaming service that needs to be transmitted and received, or when handover occurs, handover failure, or RLF (radio link failure) frequently occurs for a specific terminal or a specific cell), and candidate cell information includes information necessary for fast HO It can be transmitted to the terminal.

At this time, the base station may transmit new UE-Identity, radioResourceConfigCommon, rach-ConfigDedicated, and ReuseProtocolType information as information required for fast HO. In addition, as described above, the base station may transmit only information necessary for fast HO and inform the UE about a target cell to perform fast HO indefinitely, whereas the base station explicitly includes a fast HO indication. It may be transmitted to the terminal.

Accordingly, the UE may perform fast HO when the handover event is triggered and additional information for fast HO is included in the candidate cell information for the target cell performing the handover.

If it is determined that fast HO is performed, in step S540, the UE reuses an existing PDCP security key and a radio bearer (RB) of a specific user plane protocol (eg PDCP / RLC) (No reset). )can do.

Specifically, the terminal performing the fast HO does not reset the RB of the specific user plane protocol (for example, PDCP / RLC) and maintains the security key as the security key used in the source cell.

In operation S550, the terminal may perform a random access procedure with the target cell. In detail, the terminal may perform dedicated random access or contention-based random access according to whether or not rach-ConfigDedicated is set to the received candidate cell information.

When the random access procedure is normally completed, the handover complete message including the C-RNTI information of the candidate cell may be transmitted to the target base station. For example, the terminal may transmit an RRC reset complete message to the target base station.

On the other hand, if it is determined in step S530 that the target cell is not the target cell of the fast HO target, the terminal may proceed to step S570 to perform a general handover procedure. The general handover procedure is as described above with reference to FIGS. 1 and 2.

6 is a flowchart illustrating an inter-cell handover (UE-Based intra-HO) procedure in a terminal-based base station of a source cell according to an embodiment of the present invention.

First, in step S600, the source cell may receive a measurement report from the terminal to select a candidate target cell.

For example, if it is determined that the UE-based HO is required, the source cell may transmit a measurement configuration value to the terminal for selecting a candidate cell. The source cell receives the measurement report from the terminal according to the set value.

In step S610, the source cell may transmit candidate target cell information for the UE-Based HO to the terminal.

For example, the source cell transmits, to the UE, information about a candidate cell that can become a target cell in the UE-based HO based on the measurement report information. The candidate cell information may include information for the UE to determine whether fast HO is required for each candidate cell as described above with reference to Table 1.

In step S620, the terminal and the target cell may perform a random access procedure. Specifically, when a handover event is triggered in the terminal and one of the candidate cells in the base station is selected as the target cell, the terminal may perform a random access procedure with the target cell.

In operation S630, the target cell may determine whether a handover complete message including a new terminal identifier for fast handover is received from the terminal. If it is determined that the handover complete message including the new terminal identifier is received, the target cell in step S640 is an RB (radio) of an existing source cell security key and a specific User Plane Protocol (eg PDCP / RLC). bearer) can be reused.

For example, if a fast HO is determined based on candidate cell information in the terminal, the terminal may receive a handover complete message including a new terminal identifier for fast HO to the target cell.

When the handover complete message including the new terminal identifier is received, the target cell may recognize the terminal as a terminal through which handover is performed through fast HO. Therefore, the target cell can be reused without resetting the security key of the existing source cell and the RB of a specific User Plane Protocol (eg PDCP / RLC).

On the other hand, in step S630, when the target cell does not receive a handover complete message including the new terminal identifier, for example, when receiving an RRC connection reestablishment request message, step Proceeding to S650, a general handover procedure may be performed.

Meanwhile, FIG. 7 is a flowchart illustrating a UE-based inter-HO procedure based on a terminal of a base station according to an embodiment of the present invention. For example, the source cell may be a cell of the source base station, and the target cell may be a cell of a target base station different from the source base station.

First, in step S700, the source cell may receive a measurement report from the terminal to select a candidate target cell.

In operation S710, the source cell may transmit radio bearer (RB) and security key information of a specific user plane protocol (eg PDCP / RLC) to the target cell. For example, the target cell may reuse the received RB and security key information of a specific user plane (eg PDCP / RLC) when the connection with the terminal is completed.

In operation S720, when an ack signal for the transmission is received from the target cell, in operation S730, the source cell may transmit candidate target cell information for terminal-based handover to the terminal.

The terminal, which has received the information of the target cell for the fast HO by the source cell, may perform the fast HO to the target cell. Accordingly, the terminal can reuse the RB and security key of a specific user plane protocol (eg PDCP / RLC).

On the other hand, in step S740, the target cell of the terminal and the target base station may perform a random access procedure. In operation S750, the target cell may determine whether a handover complete message including a new terminal identifier for fast handover is received from the terminal.

For example, when fast HO is performed, the terminal may transmit a new terminal identifier in the handover complete message. Therefore, based on whether the handover complete message including the new terminal identifier is received, the target cell can determine whether to perform fast HO.

Thus, in step S760, the target cell may reuse the existing source cell security key and the RB of a particular User Plane Protocol (eg PDCP / RLC).

In operation S770, the target cell may transmit a fast HO indication to the source cell. Specifically, since the target cell is a cell of a base station different from the source cell, the target cell may transmit the fast HO indication to inherit the existing RLC RB.

Therefore, in step S780, the source cell receiving the fast HO indication may transmit the SNstatus of the RLC to the target cell 300. Accordingly, the target cell 300 can be reused without resetting the existing RLC RB.

Meanwhile, in step S750, when the handover complete message including the new terminal ID for the fast HO is not received from the terminal, the target cell may perform a general handover procedure with the terminal. (Step S790)

Hereinafter, a procedure for performing network-based (NW-based) handover will be described in detail.

8 is a sequence diagram illustrating an NW-based intra HO procedure according to an embodiment of the present invention. Therefore, the source cell 200 and the target cell 300 of FIG. 8 may be cells of the same base station.

First, in step S810, the terminal 100 may transmit a measurement report (measurement report) to the source cell 200. For example, the terminal 100 connecting to the source cell 200 and performing communication may periodically measure the signal level and report it to the source cell 200.

In more detail, the terminal 100 may be set for a preset condition or report period for the measurement report. In addition, the terminal 100 may satisfy the preset condition or perform the measurement report according to a preset reporting period according to the setting.

In operation S820, the source cell 200 receiving the measurement report may determine the handover. In the NW-based HO, unlike the UE-based HO, the subject that determines the handover may be the source cell.

In detail, the source cell 200 may determine a target cell to perform handover based on the measurement report transmitted by the terminal 100. In addition, the source cell 200 may determine that the target cell 300 should perform fast HO. In this case, the source cell 200 may not perform RB reset and security key update of a specific user plane protocol (eg PDCP / RLC). For example, when the source cell 200 is a cell in a base station such as a cell serving as a target cell, the source cell 200 may determine to perform fast HO.

When the handover is determined, in step S830, the source cell 200 may transmit an RRC connection reconfiguration message including movement control information to the terminal 100. In this case, the source cell 200 may transmit information on the target cell 300 to perform handover to the terminal 100. As described above, when the source cell 200 determines the fast HO with the target cell 300, the source cell 200 may include fast HO indication information about the target cell 300 and transmit the fast HO indication.

Therefore, the terminal 100 receiving the RRC connection reconfiguration message performs fast HO, and thus can be reused without resetting the RB and the security key of a specific user plane protocol (for example, PDCP / RLC). For example, the terminal 100 may use the target cell 300 as it is without updating the security key used with the source cell 200.

In operation S840, the terminal 100 may transmit a random access preamble to the target cell 300. In response to the random access preamble, in step S850, the terminal 100 may receive a random access response message from the target cell 300.

In addition, in step S860, the terminal 100 may complete the connection with the target cell 300 by transmitting an RRC connection reconfiguration complete message to the target cell 300. In this case, the terminal 100 may transmit the RRC connection reset complete message, including the new terminal identifier.

Accordingly, the target cell 300 receiving the new terminal identifier may reuse the security key of the existing source cell and the RB of a specific user plane protocol (eg PDCP / RLC).

9 is a sequence diagram illustrating an NW-based inter HO procedure according to an embodiment of the present invention.

First, in step S910, the terminal 100 may transmit a measurement report to the source cell 200. For example, the terminal 100 connecting to the source cell 200 and performing communication may periodically measure the signal level and report it to the source cell 200.

In operation S920, the source cell 200 that has received the measurement report may determine handover. For example, the source cell 200 may determine the target cell and determine whether to perform fast HO. When the target cell to be handed over satisfies a preset condition, the source cell 200 may determine to perform fast HO.

If the fast HO is determined, in step S930, the source cell 200 may transmit a handover request to the target cell 300 on which the handover is to be performed. In this case, the source cell 200 may transmit the RB and the security key of a specific user plane protocol (for example, PDCP / RLC) to the target cell 300.

In operation S940, the target cell 300 that determines that the handover is acceptable may transmit a handover request response to the source cell 200.

In operation S950, the source cell 200 receiving the ack response may transmit an RRC connection reconfiguration message including movement control information to the terminal 100. In this case, the source cell 200 may transmit information on the target cell 300 to perform handover to the terminal 100. For example, the source cell 200 may include fast HO indication information about the target cell and transmit it to the terminal 100.

Accordingly, the terminal 100 receiving the RRC connection reconfiguration message may reuse the RB and the security key of a specific user plane protocol (eg PDCP / RLC).

In operation S960, the source cell 200 may transmit SNstatus to the target cell 300. Specifically, the source cell 200 transmits the sequence number of the packet of the RLC layer to the target cell 300 through the interface between the base stations, to inform which packet to transmit and receive from the terminal 100 after the handover is completed. Can be. The source cell 200 may forward the data packet having the SN following the SN of the data packet transmitted from the source cell to the target cell according to the SNstatus of the RLC.

The terminal 100 and the target cell 300 may perform a random access procedure. In detail, in operation S970, the terminal 100 may transmit a random access preamble to the target cell 300. In response to the random access preamble, in step S980, the terminal 100 may receive a random access response message from the target cell 300.

In addition, in step S990, the terminal 100 may complete the connection with the target cell 300 by transmitting an RRC connection reconfiguration complete message to the target cell 300. In this case, the terminal 100 may transmit the RRC connection reset complete message, including the new terminal identifier.

Hereinafter, detailed operations of the terminal and the base station in the NW-based fast HO as described above will be described with reference to FIGS. 10 to 12.

Specifically, FIG. 10 is a flowchart illustrating an NW-based fast HO procedure of a terminal according to an embodiment of the present invention. When the UE performs the NW-based fast HO, it may operate regardless of intra or inter HO.

First, when a network-based handover event is triggered in step S1000, in step S1010, the terminal may transmit a measurement report to the source cell. In operation S1020, a handover command message including fast handover indication information may be received from the source cell.

In detail, the terminal transmits the measurement report to the source cell due to the triggering of the HO event. The source cell may transmit a HO command including information on a target cell and whether fast HO is performed to the terminal.

In step S1030, the terminal may determine whether it is a fast HO target target cell. For example, when the terminal receives information required for fast HO through target cell information, the terminal may determine that the target cell is a fast HO target target cell. According to an embodiment of the present invention, when handover (intra-HO) between cells in one base station is performed, the source cell may determine that the fast HO condition is satisfied. Accordingly, a terminal that receives target cell information including information required for the fast HO at intra-HO may perform fast HO on the target cell.

Meanwhile, if it is determined that the target cell is a fast HO target, in step S1040, the terminal may maintain the key used in the source cell without resetting the RB of the specific User Plane Protocol (eg, PDCP / RLC).

In operation S1050, the terminal may perform a random access procedure with the target cell.

When the handover procedure is completed, in step S1060, the terminal may transmit a HO complete message (eg, RRC reset complete message) including the new terminal identifier to the target cell.

If it is determined in step S1030 that it is not a fast HO, the terminal proceeds to step S1070 to perform a general handover procedure.

11 is a flowchart illustrating an NW-based intra-HO procedure of a base station according to an embodiment of the present invention.

First, in step S1100, the source cell may receive a measurement report due to a handover event trigger from the terminal. In operation S1200, the source cell may determine handover. In detail, the source cell may determine a target cell to perform handover based on the received measurement report.

In operation S1120, the source cell may determine whether fast HO is required for the determined target cell. For example, the source cell may determine that the fast HO is necessary when the service used by the terminal performing the communication is a service such as streaming that needs to seamlessly transmit and receive data. Alternatively, if it is determined that the handover is repeated frequently for a certain time, the source cell may determine that a fast HO is required for the terminal.

If it is determined that fast HO is required for the determined target cell, in step S1130, the source cell may not perform RB reset and security key update of a specific User Plane Protocol (eg PDCP / RLC). Can be.

Accordingly, in step S1140, the source cell may transmit to the HO command message terminal including fast HO indication information.

In operation S1150, a random access procedure between the terminal and the target cell may be performed.

When the HO procedure is completed, in step S1160, the target cell may receive a HO complete message (eg, RRC reset complete message) including the new terminal identifier from the terminal.

Accordingly, in step S1170, the target cell may reuse an existing source cell security key and a radio bearer (RB) of a specific User Plane Protocol (eg PDCP / RLC). For example, the target cell may not reset a radio bearer of a security key and a specific user plane protocol (eg PDCP / RLC) when the terminal performs fast HO through the new terminal identifier. Can be.

On the other hand, if it is determined in step S1120 that fast HO is not necessary, the process proceeds to step S1180 where the terminal and the target base station can perform a general handover procedure.

12 is a flowchart illustrating an NW-based inter-HO procedure of a base station according to an embodiment of the present invention. The NW-based inter-HO procedure shown in FIG. 12 is similar to the NW-based intra-HO procedure of FIG. 11 described above. However, in FIG. 12, since the source cell and the target cell are cells of different base stations, an additional operation may exist.

First, in step S1200, the source cell may receive a measurement report due to a handover event trigger from the terminal. In operation S1210, the source cell may determine handover. In detail, the source cell may determine a target cell to perform handover based on the received measurement report.

In operation S1220, the source cell may determine whether fast HO is required for the determined target cell.

If it is determined that the fast HO is necessary for the determined target cell, in step S1230, the source cell transmits RB and security key information of a specific user plane protocol (eg PDCP / RLC) of the target base station. Can be sent to the target cell.

The target cell receiving the RB and security key information of the specific User Plane Protocol (eg PDCP / RLC) may transmit an ack signal to the source cell (step S1240).

In operation S1250, the source cell may transmit a HO command message terminal including fast HO indication information. Therefore, when the UE performs a handover to a target cell that needs to perform fast HO, the UE may reuse an RB and a security key of a specific user plane protocol (eg, PDCP / RLC).

In operation S1260, the source cell may transmit an RLC sequence number status (SN status) to the target cell. Specifically, the source cell may transmit the sequence number of the packet of the RLC layer to the target cell through the interface between the base stations, to inform which packet to transmit and receive from the terminal 100 after completion of the handover.

In operation S1270, a random access procedure between the terminal and the target cell may be performed.

When the HO procedure is completed, in step S1280, the target cell may receive a HO complete message (eg, RRC reset complete message) including the new terminal identifier from the terminal.

Accordingly, in step S1290, the target cell may reuse the existing source cell security key and radio bearer (RB) of a specific User Plane Protocol (eg PDCP / RLC). For example, the target cell may not reset a radio bearer of a security key and a specific user plane protocol (eg PDCP / RLC) when the terminal performs fast HO through the new terminal identifier. Can be.

On the other hand, if it is determined in step S1220 that no fast HO is required, the process proceeds to step S1295 where the terminal and the target base station can perform a general handover procedure.

By the handover method as described above, in the aspect of processing and mobility in the Cloud RAN (Centralization & Virtualization) environment by removing the cell's dependency and removing unnecessary RRC messages in the Cipering and RRC reset operations This has the effect of improving performance.

FIG. 13 is a block diagram illustrating a configuration of a terminal 1300 according to an exemplary embodiment. The terminal 1300 may include a transceiver 1310 and a controller 1320.

The transceiver 1310 is a component for transmitting and receiving signals.

The controller 1320 is a component for overall control of the terminal 1300. In detail, the controller 1320 may control the transceiver 1310 to receive a message including information on at least one target cell for performing a fast handover from a source cell.

The controller 1320 may control to perform the fast handover by reusing a radio bearer based on previously received information.

In addition, the controller 1320 may perform the fast handover by reusing a security key corresponding to the source cell and a radio bearer of a specific user plane protocol (eg, PDCP / RLC).

When the fast handover procedure is completed, the controller 1320 may control the transceiver 1310 to transmit a handover complete message including a new terminal identifier to the target cell. A security key corresponding to the source cell and a radio bearer of a specific user plane protocol (eg PDCP / RLC) are reused by the target cell receiving the handover complete message including the new terminal identifier. You can do

The controller 1320 may control not only the above contents but also the operation of the terminal 1300 in all the above-described embodiments.

14 is a block diagram illustrating a configuration of a base station 1400 according to an embodiment of the present invention. The base station 1400 may include a transceiver 1410 and a controller 1420.

The transceiver 1410 is a component for transmitting and receiving signals.

The controller 1420 is a component for controlling the base station 1400 as a whole.

First, the base station 1400 may perform fast HO between a source cell and a target cell in a cell. In this case, the controller 1420 may be included in each of the source cell and the target cell to control the operation of each cell. However, this is only an example, and the controller 1420 may be included in the base station 1400 to control operations of the source cell and the target cell.

First, when the control unit 1420 is a control unit of the source cell or the base station 1400, the control unit 1420 receives the transmission and reception unit 1410 to receive a measurement report including a measurement result for at least one cell from the terminal. Can be controlled. The controller 1420 may determine at least one target cell capable of performing fast handover for reusing the radio bearer based on the measurement report.

For example, the controller 1420 may determine another cell in the base station 1400 as a target cell to perform fast HO based on the measurement report.

In addition, the controller 1420 may control the transceiver to transmit the information on the determined at least one target cell to the terminal.

Meanwhile, when performing the fast handover, a security key corresponding to the source cell and a radio bearer of a specific user plane protocol (eg PDCP / RLC) may be reused by the terminal and the target cell.

In addition, when the control unit 1420 is a control unit of the base station 1400, the control unit 1420 is a target cell in which the fast handover is performed in the at least one target cell, the base station of the same base station as the source cell. In the case of a cell, it may be controlled to skip an RB reset of the security key and the specific User Plane Protocol (eg PDCP / RLC). Such an operation may be performed by the controller of the target cell when the controller of the target cell exists separately.

Meanwhile, when the target cell on which the fast handover is performed is a cell of a base station different from the source cell, and the controller 1420 is a controller of the source cell, the security key and the specific user plane protocol ( For example, the transceiver 1410 may be controlled to transmit information on a radio bearer of PDCP / RLC.

In the at least one target cell, when the control unit 1420 is a control unit of a source cell when the target cell on which the UE performs the fast handover is a cell of a base station different from the source cell, the sequence number state of the RLC ( The transceiver 1410 may be controlled to transmit a sequence number status to the target cell.

On the other hand, when the controller 1420 is a controller of a target cell, the controller 1420 controls the transceiver 1410 to receive a handover message including a new terminal identifier from the terminal when the fast handover is completed. Based on the new terminal identifier of the received message, to reuse a radio bearer of a security key and packet data convergence protocol (PDCP) and radio link control (RLC) corresponding to a source cell; Can be controlled.

In addition, when the target cell is a cell of a base station different from the source cell, the controller 1420 controls the transceiver 1410 to receive information about the security key and the PDCP / RLC radio bearer. Based on the received information, it may be controlled to reuse the security key corresponding to the source cell and the PDCP / RLC radio bearer.

When the target cell is a cell of a base station different from the source cell, the controller 1420 may control the transceiver 1410 to receive an RLC sequence number status from the source cell.

When the source cell and the target cell are cells of separate base stations, the above operations may be performed by the controllers of the cells.

The controller 1420 may control not only the above contents but also the operation of the base station 1400 in all the above-described embodiments.

The above components of the terminal and the base station may be implemented in software. For example, the control unit of the terminal and the base station may further include a flash memory or other nonvolatile memory. The nonvolatile memory may store a program for performing each role of the controller.

In addition, the control unit of the terminal and the base station may be implemented in a form including a CPU and a random access memory (RAM). The CPU of the controller may copy the above-described programs stored in the nonvolatile memory into the RAM and then execute the copied programs to perform the functions of the terminal as described above.

The control unit is a component in charge of controlling the terminal and the base station. The controller may be used interchangeably with the same meaning as a central processing unit, a microprocessor, a processor, an operating system, and the like. In addition, the control unit of the terminal and the base station may be implemented as a single chip system (System-on-a-chip or System on chip, SOC, SoC) together with other functional units, such as a communication module included in the terminal.

Meanwhile, the method of the terminal and the base station according to the various embodiments described above may be coded in software and stored in a non-transitory readable medium. Such non-transitory readable media can be mounted and used in a variety of devices.

The non-transitory readable medium refers to a medium that stores data semi-permanently and is readable by a device, not a medium storing data for a short time such as a register, a cache, a memory, and the like. Specifically, it may be a CD, a DVD, a hard disk, a Blu-ray disk, a USB, a memory card, a ROM, or the like.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims

A terminal in a wireless communication system,

Transmitting and receiving unit for transmitting and receiving a signal; And

Controlling the transceiver to receive a message including information on at least one target cell for fast handover from a source cell, and reusing a radio bearer based on previously received information to reuse the fast handover; A controller for performing over; Terminal comprising a.
The method of claim 1,

The control unit,

Security key and service data adaptation protocol (SDAP) corresponding to the source cell, packet data convergence protocol (PDCP), radio link control (RLC), media access control ( and performing the fast handover by reusing a radio bearer of a medium access control or a physical layer.
The method of claim 1,

The control unit,

When the fast handover procedure is completed, the transceiver is controlled to transmit a handover complete message including a new terminal identifier to the target cell.

And a security key corresponding to the source cell and a radio bearer of a specific user plane are reused by the target cell receiving the handover complete message including the new terminal identifier.
In a source cell in a wireless communication system,

Transmitting and receiving unit for transmitting and receiving a signal; And

At least one target capable of performing a fast handover to control the transceiver to receive a measurement report including a measurement result for at least one cell from a terminal and to reuse a radio bearer based on the measurement report A controller which determines a cell and controls the transceiver to transmit information about the determined at least one target cell to a terminal; Source cell comprising a.
The method of claim 4, wherein

When performing the fast handover,

Security key and service data adaptation protocol (SDAP) corresponding to the source cell, packet data convergence protocol (PDCP), radio link control (RLC), media access control ( A source cell, wherein the radio bearer of the medium access control or the physical layer is reused by the terminal and the target cell.
The method of claim 4, wherein

The control unit,

In the at least one target cell, when the target cell on which the fast handover is performed with the terminal is a cell of a base station such as the source cell, the security key and the RB reset of the specific user plane are skipped, and If the target cell on which the fast handover is performed is a cell of a base station different from the source cell, the source and control unit for controlling the transceiver to transmit information about the security key and the radio bearer of the specific user plane to the target cell Cell.
The method of claim 4, wherein

The control unit,

In the at least one target cell, when the terminal and the target cell where the fast handover is performed are cells of a base station different from the source cell, the transceiver unit to transmit a sequence number status of an RLC to the target cell A source cell, characterized in that for controlling.
In a target cell in a wireless communication system,

Transmitting and receiving unit for transmitting and receiving a signal; And

Upon completion of the fast handover, controlling the transceiver to receive a handover message including a new terminal identifier from the terminal, and adapting a security key and service data corresponding to a source cell based on the new terminal identifier of the received message. Protocol (Service Data Adaptation Protocol, SDAP), packet data convergence protocol (PDCP), radio link control (RLC), medium access control or physical layer A control unit for reusing a radio bearer; Target cell containing.
The method of claim 8,

The control unit,

If the target cell is a cell of a base station different from the source cell, the transceiver is controlled to receive information about the security key and the radio bearer of the specific user plane, and corresponds to the source cell based on the received information. The target cell, characterized in that for controlling to reuse the security key and the radio bearer of the specific user plane.
The method of claim 8,

The control unit,

And when the target cell is a cell of a base station different from the source cell, controlling the transceiver to receive an RLC sequence number status from the source cell.
In the handover method of the terminal in a wireless communication system,

Receiving a message from the source cell, the message including information on at least one target cell for performing fast handover; And

Based on the received information, reusing a radio bearer to perform the fast handover.
The method of claim 11,

The step of performing,

Security key and service data adaptation protocol (SDAP) corresponding to the source cell, packet data convergence protocol (PDCP), radio link control (RLC), media access control ( performing the fast handover by reusing a radio bearer of a medium access control or a physical layer;

When the fast handover procedure is completed, transmitting a handover complete message including a new terminal identifier to the target cell; More,

And by the target cell receiving the handover complete message including the new terminal identifier, a security key corresponding to the source cell and a radio bearer of a specific user plane.
In a handover method of a source cell in a wireless communication system,

Receiving a measurement report including measurement results for at least one cell from a terminal;

Based on the measurement report, determining at least one target cell capable of performing fast handover that reuses a radio bearer; And

Transmitting the information on the determined at least one target cell to a terminal; Method comprising a.
The method of claim 13,

When performing the fast handover,

Security key and service data adaptation protocol (SDAP) corresponding to the source cell, packet data convergence protocol (PDCP), radio link control (RLC), media access control ( A radio bearer of medium access control or physical layer is reused by the terminal and the target cell.

In the at least one target cell, transmitting a sequence number status of an RLC to the target cell when the target cell to which the fast handover is performed is a cell of a base station different from the source cell;

Skipping, in the at least one target cell, an RB reset of the security key and the specific user plane when the target cell to which the fast handover is performed is a cell of a base station such as the source cell; And

When the target cell on which the fast handover is performed is a cell of a base station different from the source cell, transmitting information about the security key and the radio bearer of the specific user plane to the target cell; Method further comprising a.
In a handover method of a target cell in a wireless communication system,

When the fast handover is completed, receiving a handover message from the terminal including a new terminal identifier; And

Based on the new terminal identifier of the received message, a security key corresponding to a source cell and a Service Data Adaptation Protocol (SDAP), a packet data convergence protocol (PDCP), and a radio link control reusing a radio bearer of a radio link control (RLC), a medium access control, or a physical layer; How to include.